Re: 4.9-rc1 boot regression, ambiguous bisect result

From: Dan Williams <dan.j.williams@intel.com>
To: Ingo Molnar <mingo@kernel.org>
Cc: Matt Fleming <matt@codeblueprint.co.uk>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-efi@vger.kernel.org, Peter Jones <pjones@redhat.com>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>
Subject: Re: 4.9-rc1 boot regression, ambiguous bisect result
Date: Fri, 21 Oct 2016 11:20:12 -0700	[thread overview]
Message-ID: <CAPcyv4iijpLxn-s0Q-x+23y=+y4tUHcWqdET0R07rzmbbBgSKg@mail.gmail.com> (raw)
In-Reply-To: <20161021070054.GA6301@gmail.com>

On Fri, Oct 21, 2016 at 12:00 AM, Ingo Molnar <mingo@kernel.org> wrote:
>
> * Dan Williams <dan.j.williams@intel.com> wrote:
>
>> On Thu, Oct 20, 2016 at 8:22 AM, Dan Williams <dan.j.williams@intel.com> wrote:
>> > On Thu, Oct 20, 2016 at 5:29 AM, Matt Fleming <matt@codeblueprint.co.uk> wrote:
>> >> On Wed, 19 Oct, at 09:04:29PM, Dan Williams wrote:
>> >>> Hi,
>> >>>
>> >>> I am currently unable to boot a Yoga 900 with latest mainline, but 4.8 boots.
>> >>>
>> >>> The symptom is a reboot before the video console is available.
>> >>>
>> >>> I bisected to commit 816e76129ed5 "efi: Allow drivers to reserve boot
>> >>> services forever".  However, that commit is known to be broken.  The
>> >>> proposed fix, commit 92dc33501bfb "x86/efi: Round EFI memmap
>> >>> reservations to EFI_PAGE_SIZE", also exhibits the reboot problem.
>> >>>
>> >>> During the bisect some of the stopping points landed on commits that
>> >>> caused the boot process to hang rather than cause a reboot.  The
>> >>> commits that resulted in a hang are marked "git bisect skip" in this
>> >>> log: https://gist.github.com/djbw/1b501daa98192a42ae848f03bb59c30e
>> >>>
>> >>> I'll try treating those hangs as bad bisect results and re-run the
>> >>> full bisect tomorrow.  In the meantime I wonder if the bisect log
>> >>> implicates a better regression candidate?
>> >>
>> >> Could you mail the dmesg output when booting a known working kernel
>> >> with efi=debug ?
>> >
>> > Here it is:
>> >
>> > https://gist.github.com/djbw/cae05e721b159d5ad7b146d7a93f5fa2
>>
>> I am able to build a kernel and boot the platform with the following
>> set of reverts:
>>
>>       Revert "x86/efi: Round EFI memmap reservations to EFI_PAGE_SIZE"
>>       Revert "x86/efi-bgrt: Use efi_mem_reserve() to avoid copying image data"
>>       Revert "efi/esrt: Use efi_mem_reserve() and avoid a kmalloc()"
>>       Revert "efi: Allow drivers to reserve boot services forever"
>
> Could you please describe the bootup behavior after each revert? I.e. wild guess:
>
>        vanilla kernel:
>    # spontaneous reboot
>        + Revert "x86/efi: Round EFI memmap reservations to EFI_PAGE_SIZE":
>    # spontaneous reboot
>        + Revert "x86/efi-bgrt: Use efi_mem_reserve() to avoid copying image data":
>    # hang
>        + Revert "efi/esrt: Use efi_mem_reserve() and avoid a kmalloc()":
>    # hang
>        + Revert "efi: Allow drivers to reserve boot services forever":
>    == works
>
> ?

In this case all but the last revert produce the same result, instant
reboot after loading the kernel.  I have not been able to pinpoint
what changes that behavior to the hang conditions I saw mid-bisect.

The first three reverts are just there to get the kernel to build
again after reverting "efi: Allow drivers to reserve boot services
forever"